1. Field of the Invention
This invention relates to an information medium, and a method and a system for reading the information wherein pattern of the information recorded at a high density can be readily reproduced.
2. Prior Art
Magnetic recording and optical recording have been employed for the purpose of high density recording. Hard disc drives and magnetic tape drives are typical magnetic recording systems, and magnetooptical recording system and phase change recording system are typical optical recording systems.
Such conventional recording using the magnetic and optical systems, however, suffer from signal detection limit intrinsic to the respective systems.
For example, in the case of the magnetic recording, reduction in size of the record marks invites disappearance of the record marks (reversely magnetized areas) even at room temperature due to instabilization of magnetic domain walls by thermal perturbation. In the case of hard disc drives wherein magnetoresistance effect element is used for the reading, reduction in size of the record marks results in reduced fluctuation of the magnetic field intensity, and a detection limit is also imposed in this respect.
On the other hand, in the case of the optical recording, signal detection limit is imposed by the diffraction limit determined by the wavelength of the light used for reading and numerical aperture of the reading optical system.
In view of such situation, Japanese Patent Kokai No. (JP-A) 1998/172187 proposes use of a medium comprising a charge storage material wherein recording and erasure is effected by charge transfer, and the information recorded is reproduced by detecting fluctuation in charge, surface potential, or capacitance using a scanning probe microscope (SPM).
The recording medium and the recording method described in JP-A 1998/172187 are not very easy to accomplish in general use. In an embodiment of JP-A1998/172187, the medium comprises a conductive silicon substrate and a silicon oxide film, a silicon nitride film, and a silicon oxide film disposed in this order on the substrate to form a charge storage layer, and the recording is effected by creating potential difference on the medium through charge transfer using an atomic force microscope (AFM).
In view of the situation as described above, an object of the present invention is to provide an information medium wherein the information can be recorded at a high density in a convenient manner, and the information recorded at such high density can be reproduced in a convenient manner. Another a object of the present invention is to provide a method for reproducing the information recorded in such medium, and a system for reproducing the information wherein such method is utilized.
Such objects are attained by the present invention as described in (1) to (4), below.
(1) An information medium wherein the information recorded is read by reading difference in crystallographic state, crystallographic phase or constituent material as a difference in surface potential or surface charge density.
(2) A method for reading information recorded in a medium wherein the information is read by reading difference in crystallographic state, crystallographic phase or constituent material as a difference in surface potential or surface charge density.
(3) A method for reading information according to the above (2) wherein the method is applied to a phase change recording medium, and difference between crystalline region and amorphous region is read as a difference in surface potential or surface charge density.
(4) A system for reading information recorded in a medium wherein the information is read by reading difference in crystallographic state, crystallographic phase or constituent material as a difference in surface potential or surface charge density.